Macrophages induce angiogenesis, the process of new capillary blood vessel formation in a number of important pathophysiological processes yet the regulatory mechanisms that control expression of this vital function are still poorly understood. The overall objective of this study is to use somatic cell hybrids to investigate the mechanisms which regulated expression of macrophages angiogenic activity (AA). The specific aims are: (1) to test the hypothesis that the ability of macrophages to express AA is a recessive trait, subject to trans-acting suppression by unactivated or undifferentiated macrophages, (2) to determine if suppression and re-expression of AA parallels suppression and re-expression of certain endothelial cell functions (proliferation, directional migration and plasminogen activator (PA) activity) associated with new capillary formation, (3) to determine if trans-acting suppression of AA can be reversed by stimuli known to activated macrophages and (4) to identify specific chromosomes carrying genes involved in the induction and suppression of macrophages AA. Cells will be fused with polyethylene glycol (PEG-1000) and hybrids will be grown and selected in HAT or HAT-Oubain medium. Media conditioned by hybrids will be assayed for AA on the chick chorioallantoic membrane (CAM) and in the rat cornea. Proliferation, directional migration and PA activity will be assayed with cultures of bovine adrenal gland capillary endothelial cells (BCE) by direct cell counts, measuring migration under agarose and by assaying release of radioactivity from 125I- labelled fibrin plates. Re-induction of AA in hybrid will be evaluated following exposure of cells to lipopolysaccharide (LPS). Chromosomes carrying genes involved in the induction and suppression of AA will be determined by karyotyping trypsin/Giemsa G banded metaphase chromosomes. The results of this study will provide greater insight into (1) how expression of AA is controlled during differentiation and activation of macrophages, (2) the mechanism underlying the unregulated expression of AA in neoplastic cells and (3) allow for the development and eventual implementation of novel molecular approaches for the treatment of disease processes when microvascular proliferation has been shown to contribute to their pathogenesis.